A major cost problem experienced by the electronics industry is the loss of solderability of electronic components and printed circuit boards, particularly during storage. Poor solderability of component leads and printed wiring boards is believed to account for as much as 75% of solder joint failures. Because humid environments are known to exacerbate the problem, an electrochemical mechanism is clearly the cause of solderability degradation. In the lead-tin-copper solder system, for example, previous studies have determined that oxidation of the tin-lead (Sn--Pb) surface and underlying copper-tin (Cu--Sn) intermetallic layers is involved in the degradation process.
A traditional method of removing metallic oxides is the use of aggressive acids to dissolve the detrimental oxides. This method is undesirable for use with printed circuit boards, however, because the acids also attack the circuit board and component materials while dissolving the metallic oxides. Also, anions from such acids (e.g., chloride) can become incorporated in gummy flux residues. Such residues are difficult to remove completely, and they can cause corrosion and subsequent component failure. The alternative high-temperature oxide reducing processes known in the prior art are also destructive of component materials and thus unsuitable for use with printed wiring boards and electronic components.
Because degradation of solderability involves an electrochemical oxidation mechanism, it is believed that solderability of electronic components can be restored by reversing the process with a method that electrochemically reduces the detrimental metallic oxides. The availability of a low-temperature method for restoring the solderability of electronic circuitry and component leads will result in significant savings for the electronics industry and improved reliability of systems containing soldered components. Thus, there is a need for a low-temperature, nondestructive method that restores and ensures the solderability of electronic components and printed wiring boards.